1. Field of the Invention
This invention relates to a roto-dynamic pump and more particulary a roto-dynamic pump having a recirculating means for eliminating pump cavitation.
2. Background
Roto-dynamic pumps are subjected to cavitation surges to low flow rates and at moderate to low values of net positive suction head. Low flow rates are generally flow rates of less than about 50% of maximum flow rate of the pump. Moderate to low values of net positive suction head (NPSH) are generally those that produce a pump pressure rise reduction of 1% to 3% below the pressure rise obtained in the absence of NPSH influence. In NASA publication NASA SP-8502 entitled "Liquid Rocket Engine Turbopump Inducers", May 1971, a design configuration on pages 33 and 34 is shown which attempts to contain backflow which occurs at low flow. This design, while containing backflow, has a structure protruding into the suction inlet of the pump which decreases the efficiency of the pump.
U.S. Pat. No. 3,677,659 to Williams shows a roto-dynamic pump wherein a pumping chamber communicates with a suction chamber by means of a slot. The slot allows flowing fluid to pass to the suction chamber and then to an inlet scroll for recirculation which tends to reduce pump cavitation.
U.S. Pat. No. 3,090,321 to Edwards relates to a vapor separation pump which has an arrangement of diffuser passages or openings which serve as vapor discharge outlets at low rates of flow and as secondary or auxiliary inlets at high rates of flow. The diffuser passages adjacent to the pump inlet are normally intended to function as vapor outlet openings.
U.S. Pat. No. 2,832,292 also to Edwards shows a roto-dynamic pump having a radially extending passage containing diffusion vanes which act as a vapor discharge or a secondary inlet. A lip at the end of the passage directs the discharge away from axial inlet.
U.S. Pat. No. 2,660,366 to Klein et al. pertains to fluid compressors of both the radial and axial flow types and to structural means and method of inhibiting surging in fluid flow in such compressors.